JP7178271B2 - Artificial graphite material, method for producing artificial graphite material, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to an artificial graphite material, a method for producing an artificial graphite material, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

Lithium ion secondary batteries are used in industries such as automobiles and power storage for grid infrastructure.
Graphite such as artificial graphite material is used as a negative electrode material for lithium ion secondary batteries (see, for example, Patent Document 1).

Batteries applied to automobiles are used in a wide temperature range from low temperatures of 0° C. or lower to high temperatures of 60° C. or higher. However, in lithium ion secondary batteries in which graphite is used as a negative electrode material, lithium metal tends to deposit on the negative electrode at a low temperature of 0° C. or less. When lithium metal deposits on the negative electrode, the amount of lithium ions that can move between the positive electrode and the negative electrode decreases. Therefore, the capacity of the lithium ion secondary battery deteriorates.

As already reported (see, for example, Non-Patent Documents 1 and 2), capacity deterioration progresses due to the difference in charge-discharge efficiency between the positive electrode and the negative electrode when lithium metal is not deposited on the negative electrode.

Japanese Patent No. 5415684

Abstracts of the 51st Battery Symposium 3G15 (November 8, 2010) "Carbon materials for negative electrodes for lithium ion secondary batteries", P. 3-4 (Realize, published on October 20, 1996) Carbon 1966 No. 47 30-34 Carbon 1969 No. 50 20-25 Carbon 1996 No. 175 249-256

A lithium ion battery using graphite as a negative electrode material has a problem of suppressing capacity deterioration due to charging and discharging at a low temperature of 0° C. or less. In particular, industrial lithium-ion batteries, which are applied in automotive applications and power storage for grid infrastructure, are problematic because they are used over a wide temperature range.

The present invention has been made in view of the above circumstances, and by using it as a material for a negative electrode for a lithium ion secondary battery, the discharge capacity is less likely to deteriorate even if charging and discharging are repeated at a low temperature of 0 ° C. or less. An object of the present invention is to provide an artificial graphite material from which a secondary battery can be obtained.
Further, the present invention provides a method for producing the above artificial graphite material, a negative electrode for a lithium ion secondary battery containing the above artificial graphite material, and a discharge even after repeated charging and discharging at a low temperature of 0 ° C. or less using this negative electrode. An object of the present invention is to provide a lithium ion secondary battery whose capacity is less likely to deteriorate.

[1] The crystallite size L (112) in the c-axis direction calculated from the (112) diffraction line obtained by X-ray wide-angle diffraction is 4 to 30 nm,
A volume-based surface area calculated by a laser diffraction particle size distribution analyzer is 0.22 to 1.70 m ² /cm ³ ,
an oil absorption of 67 to 147 mL/100 g,
The spectrum derived from carbon that appears in the electron spin resonance method measured using the X band is in the range of 3200 to 3410 gauss, and the line width of the spectrum calculated from the first derivative spectrum at a temperature of 4.8 K of the spectrum. △Hpp is 41 to 69 gauss
An artificial graphite material characterized by:

[2] A method for producing an artificial graphite material according to [1],
a step of coking the raw oil composition by a delayed coking process to produce a raw coal composition;
a step of pulverizing the raw coal composition to obtain raw coal powder;
a step of heat-treating the raw coal powder to obtain graphite powder;
and pulverizing the graphite powder.
[3] The fluid catalytic cracking residue is filled with a catalyst supporting one or more metals selected from Group 6A metals and Group 8 metals of the periodic table on an inorganic oxide support, and has an average pore diameter of 141 to 200 Å. A step of contacting the catalyst layer (A) and the catalyst layer (B) having an average pore diameter of 65 to 110 Å in this order to obtain a hydrodesulfurized first heavy oil;
A step of mixing the first heavy oil and a second heavy oil having a sulfur content of 0.4% by mass or less and not containing the first heavy oil to obtain a feedstock oil composition. and further comprising
3. The method for producing an artificial graphite material according to claim 2, wherein the content of said first heavy oil in said raw oil composition is 15 to 80% by mass.

[4] A negative electrode for a lithium ion secondary battery containing the artificial graphite material according to [1].
[5] A lithium ion secondary battery having the negative electrode according to [4].

A lithium ion secondary battery having a negative electrode containing the artificial graphite material of the present invention does not easily deteriorate in discharge capacity even after repeated charging and discharging at a low temperature of 0° C. or lower.

1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery of the present invention; FIG.

The artificial graphite material, the method for producing the artificial graphite material, the negative electrode for a lithium ion secondary battery, and the lithium ion secondary battery of the present invention are described in detail below. In addition, this invention is not limited only to embodiment shown below.

[Artificial graphite material]
The artificial graphite material of this embodiment satisfies all of the following conditions (1) to (4).
(1) The crystallite size L(112) in the c-axis direction calculated from the (112) diffraction line obtained by the wide-angle X-ray diffraction method is 4 to 30 nm.
(2) The volume-based surface area calculated by a laser diffraction particle size distribution analyzer is 0.22 to 1.70 m ² /cm ³ .
(3) Oil absorption is 67-147 mL/100 g.
(4) The carbon-derived spectrum that appears in the electron spin resonance method measured using the X band is in the range of 3200 to 3410 gauss, and the spectral line calculated from the first derivative spectrum at a temperature of 4.8 K of the spectrum. ΔHpp, which is the width, is 41 to 69 gauss.

Under the above condition (1), the crystallite size L (112) in the c-axis direction calculated from the (112) diffraction line obtained by the X-ray wide-angle diffraction method is defined in JIS R 7651 (2007) as “artificial graphite L(112) measured and calculated according to the Lattice Constant and Crystallite Size Determination of Materials. L(112) measured and calculated by this method may hereinafter be simply abbreviated as L(112).

Under the above condition (2), the volume-based surface area calculated by a laser diffraction particle size distribution analyzer is JIS Z 8819-2 (2001) "Expression of particle size measurement results-Part 2: Average from particle size distribution It is the volume-based surface area calculated according to "5.5 Calculation of volume-based surface area" in "Calculation of particle diameter or average particle diameter and moment". The volume-based surface area measured and calculated by this method may hereinafter be simply abbreviated as "volume-based surface area."

The oil absorption under the above condition (3) is the oil absorption measured and calculated according to JIS K 5101-13-1 (2004) "Oil absorption - Section 1: Refined linseed oil method". Hereinafter, it may be simply abbreviated as “oil absorption”.

ΔHpp in the above condition (4) is obtained by putting the graphite material in a sample tube, evacuating with a rotary pump, and then enclosing He gas in the sample tube to perform ESR measurement. , the intensity is 1 mW, the central magnetic field is 3360 G, the magnetic field modulation is 100 kHz, and the measurement temperature is 4.8 K. The distance between two peaks consisting of the smallest peak. Hereinafter, it may be simply abbreviated as "ΔHpp (4.8K)".

The inventors have focused on the size of the crystallite in the c-axis direction of the artificial graphite material, the volume-based surface area, the oil absorption, and ΔHpp (4.8K), and have made intensive studies, and found that the above conditions (1) to (4) By making a lithium ion secondary battery having a negative electrode containing an artificial graphite material that satisfies all of the above, it is possible to suppress the deterioration of the discharge capacity when charging and discharging are repeated at a temperature of 0 ° C. or less, and complete the present invention. reached.

The artificial graphite material satisfying condition (1) “L(112) is 4 to 30 nm” has highly developed crystals. An artificial graphite material with L(112) of 4 to 30 nm has a degree of graphitization suitable for a negative electrode of a lithium ion secondary battery. Since the larger the L(112), the larger the reversible capacity, the L(112) of the artificial graphite material is preferably 4 nm or more.
An artificial graphite material with L(112) of less than 4 nm has insufficient crystal structure development. Therefore, a lithium ion secondary battery having a negative electrode containing an artificial graphite material with L(112) of less than 4 nm is not preferable because of its small capacity (see, for example, Non-Patent Document 2).

The above condition (2) is a numerical value representing the particle size and distribution of the artificial graphite material. The artificial graphite material used for the negative electrode of the lithium ion secondary battery is generally particulate (powder). The particle size (particle size) of the artificial graphite material has a distribution. The relationship between the particle size and distribution (particle size distribution) of the artificial graphite material is expressed as a histogram (surface). The value expressing the particle size distribution of the artificial graphite material as a numerical value (point) is the volume-based surface area.

The artificial graphite material that satisfies the above condition (2) "having a volume-based surface area of 0.22 to 1.70 m ² /cm ³ " has a particle size distribution that can be used as a negative electrode material for lithium ion secondary batteries.
If the volume-based surface area is less than 0.22 m ² /cm ³ , the ratio of coarse particles having a large particle size increases, and it may not be possible to form a negative electrode with a general thickness (20 to 200 μm) and uniformity. In addition, when the volume-based surface area exceeds 1.70 m ² /cm ³ , the proportion of fine powder with a small particle size increases, and the influence of interaction such as adhesion acting between particles becomes stronger than the influence of gravity. Sometimes. Therefore, when a negative electrode mixture containing an artificial graphite material is used to form a negative electrode of a lithium ion secondary battery, it is difficult to obtain a homogeneous negative electrode mixture, which is not practical.

The above condition (3) "oil absorption is 67 to 147 mL/100 g" is an index showing the number of particles per unit weight when the above condition (2) of the volume-based surface area is satisfied.
The particle size distribution is expressed as a histogram of particle size (μm) and frequency (%), but frequency does not contain any information on the number of particles per unit weight. Similarly, the volume-based surface area obtained from the particle size distribution does not contain any information on the number of particles per unit weight.

When the oil absorption of the artificial graphite material is 147 mL/100 g or less, a lithium ion secondary battery having a negative electrode containing this material is unlikely to deposit lithium metal on the negative electrode even if charge-discharge cycles are repeated at a low temperature of 0 ° C. or less. , the discharge capacity is less likely to deteriorate. Further, when the oil absorption of the artificial graphite material is 67 mL/100 g or more, the number of particles per unit weight is large, so sufficient charge acceptance can be obtained even at a low temperature of 0° C. or less. Therefore, the charging/discharging efficiency of a lithium secondary battery having a negative electrode containing this is dramatically improved. Therefore, in a lithium-ion secondary battery having a negative electrode containing an artificial graphite material with an oil absorption of 67 mL/100 g or more, capacity deterioration due to repeated charge-discharge cycles at a temperature of 0 ° C. or less was sufficiently suppressed in practice. become a thing.

On the other hand, when a lithium secondary battery having a negative electrode containing an artificial graphite material with an oil absorption of more than 147 mL/100 g is charged and discharged at a low temperature of 0 ° C. or less, the number of cycles is reduced due to lithium metal deposition at the negative electrode during charging. The discharge capacity deteriorates rapidly every time. More specifically, in the artificial graphite material with an oil absorption of more than 147 mL/100 g, exfoliative pulverization occurs preferentially over fragmentary pulverization of graphite powder during production, and the particle shape is pulverized while flaking. , the number of particles per unit weight is increased. For this reason, in the negative electrode containing this artificial graphite material, the void volume (area where the electrolyte exists) between adjacent particles of the artificial graphite material is small, and lithium ions in the particles of the artificial graphite material generated by fragmentary pulverization of the graphite powder The edge that serves as the entrance and exit of the electrolyte is insufficient, and the ionic conductivity of the electrolyte is insufficient. As a result, cathodic polarization at the negative electrode tends to increase due to charging at a low temperature of 0° C. or lower, and lithium metal tends to precipitate, resulting in increased discharge capacity deterioration due to repeated charge-discharge cycles.

In the present specification, fragmentary pulverization of graphite powder means pulverization that accompanies breakage of chemical bonds of graphite and that cracks are generated substantially perpendicular to the plane direction of graphite.
Further, exfoliative pulverization of graphite powder means pulverization that does not involve breaking of chemical bonds of graphite, and that pulverization that causes exfoliation substantially parallel to the plane direction of graphite.

Condition (4) "The carbon-derived spectrum that appears in the electron spin resonance method measured using the X band is in the range of 3200 to 3410 gauss, and the spectrum is calculated from the first derivative spectrum at a temperature of 4.8 K. ΔHpp, which is the line width of the spectrum, is 41 to 69 gauss.” A lithium-ion secondary battery having a negative electrode containing an artificial graphite material does not easily deteriorate in discharge capacity even after repeated charge-discharge cycles at a low temperature of 0 ° C or less. .
Here, ΔHpp (4.8K) is an index representing the number of edge surfaces exposed on the particle surface of the graphite material. The reason for this will be detailed below.

ESR measurement is spectroscopic analysis that observes transitions between levels that occur when unpaired electrons are placed in a magnetic field. When a magnetic field is applied to a material with unpaired electrons, the energy levels of the material are split into two due to the Zeeman effect. The measurement is performed by sweeping the magnetic field under microwave irradiation. As the applied magnetic field increases, the energy splitting interval ΔE increases. Resonance absorption is observed when ΔE becomes equal to the energy of the irradiated microwave, and an ESR spectrum is obtained by detecting the amount of absorbed energy at this time. The ESR spectrum is usually obtained as a first-order differential spectrum, which is integrated once to obtain an absorption spectrum, and integrated twice to obtain a signal intensity. The magnitude of the signal intensity at this time is an index representing the magnitude of the unpaired electron density in the substance. Two types of unpaired electrons, localized electrons and conduction electrons, exist in the crystal of graphite material. That is, in the ESR measurement of a graphite material, the sum of microwave resonance absorption by these two types of unpaired electrons is observed as an ESR spectrum. The signal intensity obtained by integrating the obtained ESR spectrum twice serves as an index representing the magnitude of the unpaired electron density, which is the sum of the conduction electron density and the localized electron density. Here, the conduction electrons in the graphite material are unpaired π electrons that are spontaneously expressed in relation to the number of rings forming the hexagonal mesh plane and their bond forms, and can move freely within the hexagonal mesh plane. is possible (Non-Patent Documents 3 and 4).

On the other hand, the localized electrons are localized electrons existing on the edge surface of the hexagonal mesh plane laminate and are immobile electrons. Further, while the signal intensity of resonance absorption by conduction electrons has no temperature dependence, the signal intensity of resonance absorption by localized electrons increases in inverse proportion to T, which is the measurement temperature. For example, in the ESR measurement of a carbon material in the temperature range of 4.2 K ≤ T ≤ 300 K, when the measurement temperature is gradually lowered from 300 K, absorption of microwaves by localized electrons begins to be observed around 50 K. , in a low temperature region of 50 K or less, the signal intensity due to localized electrons is reported to increase in inverse proportion to T, which is the measurement temperature (Non-Patent Document 5).

The ESR spectrum of a graphite material is a spectrum obtained by averaging absorption spectra of different resonance magnetic fields. Therefore, when a plurality of unpaired electrons in different states exist, that is, when a plurality of resonance absorptions occur in different magnetic fields, the ESR spectrum appears to be a broad spectrum and the linewidth ΔHpp increases. In particular, when ΔHpp is large in the low-temperature region where the contribution of localized electrons is large, it can be predicted that a plurality of states of localized electrons exist in the graphite material. The existence of a plurality of states of localized electrons can be rephrased as the existence of a plurality of states of edge planes on which localized electrons exist. From these facts, in the low temperature range of 50 K or less, ΔHpp can be said to be an index representing the number of edge surfaces exposed on the particle surface of the graphite material.

The artificial graphite material of this embodiment satisfies the above condition (4). As described above, ΔHpp, which is the line width of the ESR spectrum at the measurement temperature of 4.8 K, is an index representing the number of states of localized electrons. A larger ΔHpp indicates that a plurality of states of localized electrons exist, that is, a plurality of states of the edge surface exist. On the other hand, a smaller ΔHpp indicates a smaller number of states of localized electrons, that is, a smaller number of edge surface states.

In particular, highly crystalline graphite powder with a crystallite size L (112) of condition (1) of 4 to 30 nm has a volume-based surface area of 0.22 to 1.70 m ² /cm of condition (2). When milled to reach ³ , exfoliative milling occurs preferentially over fragmentary milling, as described above. Exfoliative pulverization is pulverization caused by applying shear stress parallel to the basal plane of the crystallites that make up the graphite particles. Among them, especially on the fracture surface on the edge side, the regularity of the three-dimensional arrangement of carbon atoms is greatly reduced, and various states of localized electrons appear. growing. Fractured pulverization, on the other hand, is pulverization that occurs when mechanical energy is applied perpendicular to the basal plane of the crystallites that make up the graphite particles. The regularity of arrangement is no less reduced than in the case of exfoliative comminution. Therefore, the ΔHpp of the graphite particles obtained by the manufacturing method described in the first invention can be regarded as an index indicating the ratio of exfoliative pulverization and fragmentary pulverization. That is, only in the case of the artificial graphite obtained by the production method, it can be considered that the smaller the ΔHpp, the higher the rate of fracturing pulverization than the probability of exfoliative pulverization.

ΔHpp (4.8K) of ordinary graphite particles pulverized to an oil absorption of 67-147 mL/100 g was generally 70 gauss or more. On the other hand, the artificial graphite material described in the first invention of the present application has a ΔHpp (4.8K) of 69 cm ⁻¹ or less, so the proportion of particles that are crushed more fracturing than the normal graphite material can be considered a higher material. Such an artificial graphite material is produced by (a) using fluid catalytic cracking residual oil treated with a specific catalyst system as a raw material oil composition, and (b) after pulverizing the raw material coal composition. The difference between the volume-based surface area (hereinafter sometimes abbreviated as raw material volume-based surface area) and the volume-based surface area after pulverizing the graphite powder after the heat treatment (hereinafter, sometimes abbreviated as graphite volume-based surface area) It can be manufactured by combining two controls of controlling.

A step of pulverizing a raw coal composition obtained by coking a raw oil composition by a delayed coking process to obtain a powder of the raw coal composition, and heat-treating the powder of the raw coal composition to obtain graphite powder. The artificial graphite material of the present embodiment, which is obtained by a manufacturing method including at least the steps of pulverizing graphite powder after heat treatment, and is compared with artificial graphite without the two controls. (Artificial graphite material that combines the above two controls) is characterized in that even if the difference in (b) is large (even if the graphite is pulverized until the volume-based surface area increases), ΔHpp (4.8K ) is that small graphite powder can be obtained. That is, it can be understood that the two controls improve the probability that the graphite powder after the heat treatment is fragmentarily pulverized. Here, the graphite volume-based surface area is the same as the volume-based surface area described in the condition (2) in this embodiment. Therefore, the graphite reference surface area is set so as to fall within the particle size distribution range of artificial graphite generally used as an artificial graphite material for lithium ion secondary battery negative electrodes, as described in the numerical range of the condition (2). do it. On the other hand, the raw material volume-based surface area may be set to a value larger than the target graphite volume-based surface area in order to pulverize the graphite powder after the heat treatment. Specifically, the oil absorption and ΔHpp (4.8K) of the artificial graphite material obtained by pulverization after the heat treatment are the oil absorption of the condition (3) and the ΔHpp (4.8K) of the condition (4). should be adjusted each time so that it falls within the range of , but a typical range is 0.22 to 1.70 m ² /cm ³ .

By the above two controls, it is possible to freely control the oil absorption and ΔHpp even within the range of the volume-based surface area of the condition (2). When the raw coal composition and the graphite powder after the heat treatment are pulverized, the difference between the raw material volume-based surface area and the graphite volume-based surface area can be controlled by controlling the respective pulverization conditions (operating conditions of the pulverizer). is. In the artificial graphite material obtained by this control, ΔHpp monotonously increases as the oil absorption increases. However, the inventors found that the relationship (a function of oil absorption to ΔHpp (4.8K)) strongly depends on the feedstock composition (using fluid catalytic cracking resid treated with a particular catalyst system). et al. Therefore, it has become possible to freely control the oil absorption and ΔHpp (4.8K) of the artificial graphite material obtained by this manufacturing method. However, in order to obtain a graphite material in which lithium metal is difficult to precipitate even if charging and discharging are repeated at 0 ° C. or lower by the production method, the above condition (4) "ΔHpp (4.8 K) is 41 to 69 gauss", and The condition (3) "oil absorption is 67 to 147 ml/100 g" must be satisfied. The reason for this will be detailed below.

As described above, as far as the artificial graphite obtained by the production method is concerned, it can be considered that the smaller ΔHpp (4.8 K) is, the more fragmentary pulverization takes precedence over the exfoliative pulverization. Therefore, when ΔHpp (4.8 K) is 41 gauss or less, the ratio of edges existing on the particle surface is very high, and when this kind of artificial graphite material is used for the negative electrode, the charging/discharging efficiency of the negative electrode decreases. It is not preferable because the accompanying cycle deterioration is large. This deterioration is caused by the increase in the proportion of the edge surfaces in the graphite particle surface, which lowers the charge/discharge efficiency of the negative electrode and increases the difference between the charge/discharge efficiency and the charge/discharge efficiency of the positive electrode. This type of deterioration mechanism is exactly the same when charging and discharging are repeated at 0° C. or lower and when charging and discharging is repeated at 0° C. or higher. On the other hand, when ΔHpp (4.8K) is 69 gauss or more, as a result of exfoliative pulverization rather than fracturing pulverization, the edge planes existing on the particle surface after pulverization show a three-dimensional arrangement of carbon atoms. However, it is not preferable because it disturbs the reversible intercalation reaction of lithium ions (becomes steric hindrance) (there are many different states of localized electrons caused by breaking chemical bonds). In a lithium-ion secondary battery in which such a graphite material is used for the negative electrode, the resistance of the negative electrode is large. Therefore, when charging and discharging are repeated at 0 ° C., lithium metal is deposited on the negative electrode, and cycle deterioration increases. I don't like it because

On the other hand, as described above, the oil absorption is an index indicating the number of particles present per unit weight. Therefore, a graphite material with an oil absorption of 67 mL/100 g or less can be considered to have a very small number of particles per unit weight. A lithium ion secondary battery using such an artificial graphite material for the negative electrode has a large resistance (lower charge acceptance), especially when charged at a low temperature of 0° C. or less, and lithium metal is deposited on the negative electrode. I don't like it because it's easy. Conversely, when the oil absorption is 147 mL/100 g or more, the number of particles per unit weight increases too much, so when formed as a negative electrode of a lithium ion secondary battery, the void volume formed between adjacent particles is inevitably smaller. Further, the ion conductivity of the electrolyte present in the negative electrode increases as the void volume of the electrode increases, and the ion conductivity of the electrolyte decreases as the temperature decreases. For this reason, lithium-ion secondary batteries in which a graphite material with an oil absorption of 147 mL/100 g or more is used for the negative electrode have particularly high negative electrode resistance at low temperatures of 0°C or lower, and charging and discharging are repeated at low temperatures of 0°C or lower. In this case, the cycle deterioration of the discharge capacity increases, which is not preferable.

Therefore, as described above, the lithium ion secondary battery having the negative electrode containing the artificial graphite material of the present embodiment is a lithium ion secondary battery having the negative electrode containing the artificial graphite material that does not satisfy the conditions (3) and (4). Compared to the secondary battery, the oil absorption is small and the ΔHpp (4.8 K) is small, so the void volume between adjacent particles is relatively large, and the ionic conductivity of the electrolyte is secured even at low temperatures. The edge surface is ensured to the extent that it is difficult for lithium metal to precipitate even after repeated charging and discharging at a low temperature of 0° C. or lower, within a range that does not significantly affect the life characteristics. Therefore, a lithium-ion secondary battery having a negative electrode containing the artificial graphite material of the present embodiment can suppress deterioration of the discharge capacity even when charging and discharging are repeated at a low temperature of 0° C. or lower.

[Method for producing artificial graphite material]
The artificial graphite material of this embodiment can be manufactured, for example, by the manufacturing method described below.
That is, a step of coking the raw oil composition by a delayed coking process to produce a raw coal composition, a step of pulverizing the raw coal composition to obtain raw coal powder, and a step of heat-treating the raw coal powder. A step of obtaining graphite powder and a step of pulverizing the graphite powder are performed.

(Step of coking the raw oil composition to produce the raw coal composition)
As the raw oil composition used in the method for producing an artificial graphite material of the present embodiment, a raw oil composition containing a first heavy oil and a second heavy oil, which will be described later, is preferable.

<First heavy oil>
The first heavy oil is fluid catalytic cracking residual oil having a sulfur content of preferably 0.5% by mass or more and less than 1.5% by mass and an aroma component of preferably 50% by mass or more and less than 90% by mass, It is obtained by a predetermined hydrodesulfurization treatment. The upper limit of the sulfur content in the fluid catalytic cracking residue is more preferably 1.0% by mass. If the sulfur content in the fluid catalytic cracking residue exceeds 1.5% by mass, it may be difficult to desulfurize the polycyclic aromatic components, which are difficult to desulfurize, even if hydrodesulfurization is performed with the catalyst system described later. .
The sulfur content can be measured according to the method described in JIS M 8813-Appendix 2:2006. Further, the lower limit of the aroma component in the fluid catalytic cracking residual oil is more preferably 70% by mass.
The contents of aroma components, saturated components and asphaltene components, which will be described later, can be measured by the TLC-FID method. In the TLC-FID method, a sample is divided into four components by thin layer chromatography (TLC) into saturated components, aroma components, resin components and asphaltene components, and then each component is detected by a flame ionization detector (FID). The components were detected, and the percentage of the amount of each component with respect to the total amount of components was used as the composition component value. First, 0.2 g±0.01 g of a sample is dissolved in 10 ml of toluene to prepare a sample solution. Using a microsyringe, 1 μl of the solution is spotted on the lower end (0.5 cm position of the rod holder) of pre-baked silica gel rod-shaped thin layer (chroma rod) and dried with a dryer or the like. Next, 10 microrods are used as one set, and the sample is developed with a developing solvent. As developing solvents, hexane is used in the first developing tank, hexane/toluene (volume ratio 20:80) in the second developing tank, and dichloromethane/methanol (volume ratio 95:5) in the third developing tank. Saturated components are eluted and developed in the first development tank using hexane as a solvent. After the first development, the aroma component is eluted and developed in the second development tank. After the first development and the second development, the asphaltene component is eluted and developed in a third development tank using dichloromethane/methanol as a solvent. The chroma rod after deployment is set in a measuring instrument (for example, "Iatroscan MK-5" (trade name) manufactured by Diayatron (currently Mitsubishi Kagaku Iatron)), and each is detected by a flame ionization detector (FID). Measure the amount of ingredients. Summing the amounts of each component gives the total component amount.

The heavy oil to be used as a raw material for the above fluid catalytic cracking residue is not particularly limited as long as the sulfur content and aroma components can satisfy the above conditions by fluid catalytic cracking, but it is preferable. is a hydrocarbon oil having a density at 15° C. of 0.8 g/cm ³ or more, such as atmospheric distillation residue, vacuum distillation residue, shale oil, tar sands bitumen, orinoco tar, coal liquefied oil, and these and heavy oil obtained by hydrorefining. The density is a value measured according to the method described in JIS K 2249-1:2011.

Atmospheric distillation residue is obtained by subjecting crude oil to an atmospheric distillation apparatus, for example, by heating under normal pressure, and depending on the boiling point of the contained fraction, gas / LPG, gasoline fraction, kerosene fraction, light oil fraction, normal pressure It is one of the fractions obtained when it is divided into distillation residue, and it is the fraction with the highest boiling point. The heating temperature varies depending on the production area of the crude oil and is not limited as long as it can be fractionated into these fractions. For example, the crude oil is heated to 320°C. Vacuum distillation residue (VR) is obtained by applying crude oil to an atmospheric distillation apparatus to obtain gas, light oil, and atmospheric distillation residue, and then applying this atmospheric distillation residue to, for example, 1.3 to 4.0 kPa ( 10 to 30 Torr), the bottom oil of the vacuum distillation apparatus obtained by changing the heating furnace outlet temperature in the range of 320 to 360°C.

As a raw material for the fluid catalytic cracking residue, in addition to the above heavy oils, relatively light oils such as straight-run gas oil, vacuum gas oil, desulfurized gas oil, and desulfurized vacuum gas oil may be contained. For example, desulfurized vacuum gas oil is preferred. Vacuum gas oil is, for example, desulfurized vacuum gas oil obtained by directly desulfurizing atmospheric distillation residue (preferably sulfur content of 500 mass ppm or less and density at 15 ° C. of 0.8 / cm ³ or more). Preferably.

The conditions for fluidized catalytic cracking are not particularly limited as long as the sulfur content and aroma components satisfy the above conditions. The pressure may be 1 to 0.3 MPa, the catalyst to oil ratio (catalyst/oil) may be 1 to 20, and the contact time may be 1 to 10 seconds. Examples of catalysts used for fluidized catalytic cracking include zeolite catalysts, silica-alumina catalysts, and these catalysts carrying precious metals such as platinum.

<Hydrodesulfurization to obtain the first heavy oil>
The first heavy oil is obtained by subjecting the fluidized catalytic cracking residual oil to a predetermined hydrodesulfurization. The hydrodesulfurization system may use, for example, a catalyst system according to JP-A-2013-209528 or JP-A-2013-209529. Specifically, the fluid catalytic cracking residual oil is filled with a catalyst supporting one or more metals selected from group 6A metals and group 8 metals of the periodic table on an inorganic oxide support, with an average pore size of 140 to 200 Å catalyst layer (A) and catalyst layer (B) with an average pore size of 80 to 110 Å, using two catalyst layers in this order, optionally, catalyst layer (A) and catalyst layer (B) ), hydrodesulfurization is further carried out using three catalyst layers which are brought into contact with the catalyst layer (C) having an average pore size of 65 to 79 Å to obtain a desulfurized fluid catalytic cracking residue. The desulfurization catalyst for heavy oil used for hydrodesulfurization in the conventional production method generally has a pore size of about 80 Å, and the polycyclic aromatic component has large steric hindrance due to its molecular size. A high desulfurization rate could not be obtained because the frequency of entry of molecules decreased and the desulfurization reaction was not sufficiently carried out. In this embodiment, by using the hydrodesulfurization system described below, many polycyclic aromatic components can be removed from the fluid catalytic cracking residual oil, and the desulfurization rate can be improved. For this reason, the fluid catalytic cracking residual oil after being treated in the hydrodesulfurization system can sufficiently obtain 2- to 3-ring aromatic components, which are considered preferable for good bulk mesophase formation.

In the hydrodesulfurization system, for example, a fixed bed reactor is filled with a predetermined catalyst to form two catalyst layers, a catalyst layer (A) and a catalyst layer (B), which will be described later. The catalyst layer (C) may be formed after (A) and the catalyst layer (B) to form three layers. In this case, hydrodesulfurization is performed by sequentially contacting the catalyst layers (A) to (B) or the catalyst layers (A) to (C) with the fluid catalytic cracking residual oil.

First, the catalyst A used for the catalyst layer (A) will be described. As the inorganic oxide support for the catalyst A, alumina, silica-alumina, alumina-boria, alumina-zirconia, alumina-titania, or a combination thereof, which accounts for 85% by mass or more of the support, can be mentioned as the main component, preferably alumina and It is silica alumina. Further, these carriers may contain 0.5 to 5% by mass of phosphorus based on the carrier. The inclusion of phosphorus is preferable because the desulfurization activity is improved.

It is important that the average pore size of catalyst A is in the range of 140-200 Å, preferably in the range of 150-180 Å. With catalyst A, a polycyclic sulfur compound with three or more rings (especially five or six rings) is nuclear-hydrogenated to destroy the three-dimensional structure of the bulky tabular polycyclic aroma, resulting in a post-stage catalyst with small pores. It facilitates desulfurization in the layer. If the average pore diameter of the catalyst A is less than 140 Å, the polycyclic sulfur compound cannot be sufficiently diffused into the catalyst pores, and a sufficient effect of nuclear hydrogenation cannot be obtained. On the other hand, if it exceeds 200 Å, the packing density of the catalyst becomes low and sufficient effect of nuclear hydrogenation cannot be obtained. In addition, in the present invention, the average pore diameter of the catalyst is a value determined by the mercury intrusion method or the BJH method.

Molybdenum or tungsten is used as the Group 6A metal supported on the carrier. Their loading is preferably 3 to 22% by weight relative to the catalyst, based on their oxides. In the case of two layers, it is more preferably 8 to 15% by mass, and in the case of three layers, it is more preferably 8 to 20% by mass. If it is less than 3% by mass, there is a tendency that sufficient desulfurization and denitrification activities cannot be obtained. On the other hand, when it exceeds 22% by mass, the metal tends to aggregate and the desulfurization activity tends to decrease. Cobalt and/or nickel are used as Group 8 metals. The supported amount thereof is preferably 0.2 to 12% by mass relative to the catalyst based on their oxides. In the case of two layers, it is more preferably 1 to 10% by mass, and in the case of three layers, it is more preferably 1 to 12% by mass.

The ratio of the catalyst layer (A) to the total catalyst packed layer is preferably 10 to 30% by volume, more preferably 15 to 25% by volume, regardless of whether the total number of catalyst packed layers is two or three. If the content is less than 10% by volume, sufficient nuclear hydrogenation effect cannot be obtained. On the other hand, if it exceeds 30% by volume, the amount of catalyst in the latter stage is reduced, resulting in insufficient desulfurization activity in the latter stage.

Next, the catalyst B used for the catalyst layer (B) will be described. As the inorganic oxide support for catalyst B, the main component accounting for 85% by mass or more of the support is alumina, silica-alumina, alumina-boria, alumina-zirconia, alumina-titania, or a combination thereof. In the case of two layers, alumina boria, silica alumina and alumina titania are preferred, and alumina boria and alumina titania are particularly preferred. In the case of three layers, they are preferably alumina and silica-alumina. Further, these carriers may contain 0.5 to 5% by mass of phosphorus based on the carrier. The inclusion of phosphorus is preferable because the desulfurization activity is improved.

It is important that the average pore size of catalyst B is in the range of 65-110 Å, preferably 70-100 Å, and even more preferably 80-95 Å for two layers. For three layers, it is important to be in the range 80-110 Å, preferably 80-100 Å. The catalyst B desulfurizes the polycyclic sulfur compound, which is nuclear-hydrogenated in the catalyst layer (A) and loses its flat bulky three-dimensional structure. If the average pore diameter of catalyst B is less than the above lower limit, these sulfur compounds cannot be sufficiently diffused into the catalyst pores, and a sufficient hydrogenation effect cannot be obtained. On the other hand, if it exceeds 110 Å, the packing density of the catalyst becomes low and a sufficient desulfurization effect cannot be obtained.

Molybdenum or tungsten is used as the Group 6A metal supported on the carrier. Their loading is preferably 15 to 22% by weight relative to the catalyst, based on their oxides. In the case of two layers, it is more preferably 17 to 20% by mass, and in the case of three layers, it is more preferably 17 to 22% by mass. If it is less than 15% by mass, there is a tendency that sufficient desulfurization activity cannot be obtained. On the other hand, when the content exceeds 22% by mass, the metal tends to aggregate and the desulfurization activity tends to decrease. Cobalt and/or nickel are used as Group 8 metals. In the case of two layers, the supported amount thereof is preferably 0.2 to 10% by mass, more preferably 1 to 8% by mass, based on the catalyst based on their oxides, and in the case of three layers, the oxides thereof. It is preferably 0.2 to 12% by mass, more preferably 1 to 12% by mass, based on the catalyst.

The ratio of the catalyst layer (B) to the total catalyst packed layer is preferably 70 to 90% by volume, more preferably 75 to 85% by volume when the total number of catalyst packed layers is two. When the total number of catalyst packed layers is three, it is preferably 40 to 80% by volume, more preferably 40 to 60% by volume. If it is less than the above lower limit value or above the above upper limit value, a sufficient desulfurization effect cannot be obtained.

Next, the catalyst C used for the catalyst layer (C) will be described. As the inorganic oxide support of the catalyst C, the main component that accounts for 85% by mass or more of the support is alumina, silica alumina, alumina boria, alumina zirconia, alumina titania, or a combination thereof, preferably alumina and It is silica alumina. Further, phosphorus may be contained in an amount of 0.5 to 5% by mass based on these carriers. The inclusion of phosphorus is preferable because the desulfurization activity is improved.

It is important that the average pore size of Catalyst C is in the range of 65-79 Å, preferably in the range of 70-79 Å. Since CLO also contains relatively small sulfur compounds of bicyclic aromatics or less, if the catalyst layers (A) and (B) alone are insufficient to desulfurize them, catalyst C efficiently removes them. It desulfurizes. If the average pore diameter of the catalyst C is less than 65 Å, these sulfur compounds cannot be sufficiently diffused into the catalyst pores, and a sufficient hydrogenation effect cannot be obtained. On the other hand, if it exceeds 79 Å, the packing density of the catalyst becomes low and a sufficient desulfurization effect cannot be obtained.

Molybdenum or tungsten is used as the Group 6A metal supported on the carrier. Their supported amount is preferably 15 to 22% by weight, more preferably 17 to 22% by weight, relative to the catalyst based on their oxides. If it is less than 15% by mass, there is a tendency that sufficient desulfurization cannot be obtained. On the other hand, when the content exceeds 22% by mass, the metal tends to aggregate and the desulfurization activity tends to decrease. Cobalt and/or nickel are used as Group 8 metals. The supported amount thereof is preferably 0.2 to 12% by mass, more preferably 1 to 12% by mass, based on the oxides.

The ratio of the catalyst layer (C) to the total catalyst packed layer is preferably 10 to 40% by volume, more preferably 20 to 40% by volume, even more preferably 20 to 35% by volume. If it is less than 10% by volume or more than 40% by volume, a sufficient desulfurization effect cannot be obtained.

Desired can be hydrodesulfurized. Specifically, first, in the catalyst layer (A), a high degree of nuclear hydrogenation is performed on the polycyclic sulfur compounds in the heavy residual oil from fluidized catalytic cracking to reduce the number of rings of the polycyclic sulfur compounds (for example, 5- and 6-ring of the aromatic ring to 3 or 4 rings). Next, in the catalyst layer (B), desulfurization of the polycyclic sulfur compounds having the number of rings reduced in the catalyst layer (A) is performed (for example, desulfurization of tri- and tetra-ring sulfur compounds). Finally, in the catalyst layer (C), the polycyclic sulfur compounds are desulfurized by hydrogenating the sulfur compounds that could not be desulfurized in the catalyst layer (B). In this way, by arranging catalysts with smaller average pore diameters in order from the upstream direction and filling them at the optimum ratio, it is possible to obtain higher desulfurization performance.

Regarding the arrangement of the catalysts, in the case of two layers, for example, catalyst layer (A) may contain molybdenum, cobalt and nickel, and catalyst layer (B) may contain molybdenum and nickel. In this case, the ratio of the catalyst layer (A) to the whole is preferably 50 to 90% by volume. If it is less than 50% by volume, the desulfurization activity is improved, but the hydrogen consumption tends to increase. On the other hand, when it exceeds 90% by volume, the desulfurization activity tends to decrease although the hydrogen consumption decreases. In the case of three layers, regarding the placement of the catalyst, the ratio of each catalyst layer to the total catalyst packed layer (0 to 1.0) and the product of the average pore diameter (Å) of the catalyst in that layer It is preferable that the sum of the values is 90 or more.
Σ [(percentage of total catalyst packed layer) × (average pore diameter)] ≥ 90

The sum of the product of the ratio of each catalyst layer to the total catalyst packed layer and the average pore diameter of the catalyst in that layer is a simple representation of the number of active points that contribute to desulfurization. Due to the moderate polycyclic sulfur compound nucleus hydrogenation effect in the layer (A), a moderate polycyclic sulfur compound desulfurization effect is obtained in the catalyst layer (B), and two or less rings in the catalyst layer (C) 95 or more is more preferable, and 98 or more is even more preferable, since a sufficient desulfurization effect can be obtained for relatively small sulfur compounds. On the other hand, the upper limit is preferably 125 or less, more preferably 120 or less, in order to prevent deterioration in desulfurization performance due to excessive proportion of the catalyst layer (A) and a decrease in the proportion of the catalyst layers (B) and (C). 115 or less is more preferable.

In the catalysts used in the catalyst layers (A) to (C), the method of supporting the metal on the carrier is not particularly limited, but impregnation is preferred.

When the catalyst for the hydrodesulfurization system as described above is used as a hydrorefining catalyst for fluid catalytic cracking residue, presulfurization treatment is performed before feeding the fluid catalytic cracking residue in order to develop the activity. The conditions for the presulfurizing treatment are as follows: the sulfurizing agent is circulated at a hydrogen partial pressure of 2 MPa or more, and the maximum temperature after heating is 240 to 380°C, preferably 250 to 350°C. When the hydrogen partial pressure is less than 2 MPa, the degree of sulfidation of molybdenum or tungsten tends to be low, resulting in low desulfurization activity and denitrification activity. Also, if the maximum temperature during presulfurization is less than 240°C, the degree of sulfurization of molybdenum or tungsten is low, and if it exceeds 380°C, coking occurs and the desulfurization activity tends to decrease. Sulfurizing agents used in the preliminary sulfurization include hydrogen sulfide, carbon disulfide, dimethyl disulfide, and the like, which are used in hydrorefining at refineries.

After the preliminary sulfurization treatment, the fluidized catalytic cracking residual oil is introduced into a fixed bed reactor equipped with a hydrodesulfurization system, and hydrodesulfurization is performed under a hydrogen atmosphere under high temperature and high pressure conditions.

The reaction pressure (hydrogen partial pressure) is preferably 4 to 12 MPa, more preferably 5 to 11 MPa. Below 4 MPa, desulfurization and denitrification tend to be significantly reduced. Moreover, if it exceeds 12 MPa, hydrogen consumption will increase and the operating cost will increase.

The reaction temperature is preferably in the range of 280-400°C, more preferably 300-360°C. If the temperature is lower than 280°C, the desulfurization and denitrification activities tend to be significantly lowered, which is impractical. Above 400°C, not only does ring-opening reaction due to thermal decomposition occur, but above 400°C catalyst deterioration becomes remarkable.

The liquid hourly space velocity is not particularly limited, but is preferably 0.2 to 3h ^-1 , more preferably 0.5 to 2h ^-1 . If it is less than 0.2 h ⁻¹ , the amount of treatment is low and the productivity is low, which is not practical. On the other hand, when it exceeds 3h ⁻¹ , the reaction temperature rises and the catalyst deteriorates quickly.

The hydrogen/oil ratio is preferably 180-700 Nm ³ /m ³ , more preferably 250-600 Nm ³ /m ³ . If the hydrogen/oil ratio is less than 180 Nm ³ /m ³ , the desulfurization activity will decrease. On the other hand, when it exceeds 700 Nm ³ /m ³ , the operating cost increases while the desulfurization activity does not change significantly.

The thus obtained first heavy oil preferably contains 20% by mass or more, more preferably 25% by mass or more, of the two-ring aromatic component. Within this range, the polycyclic aromatic components are considered to have been hydrodesulfurized. , It is possible to form a bulk mesophase suitable for obtaining an artificial graphite material composed of a microstructure with selective orientation composed of crystallites in which relatively small sized hexagonal mesh planes are stacked. In addition, the 2-ring aromatic component can be quantified by the HPLC method.

<Second heavy oil>
The second heavy oil does not contain the first heavy oil and the fluidized catalytic cracking residual oil that is the raw material oil of the first heavy oil, and preferably has a sulfur content of 0.4% by mass or less. , more preferably 0.35% by mass or less, still more preferably 0.30% by mass or less. If the sulfur content exceeds the above upper limit, development of the bulk mesophase may be inhibited, which is not preferable. The asphaltene content of the second heavy oil is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. If the asphaltene content exceeds the above upper limit, the development of the bulk mesophase may be inhibited, which is not preferable.

The saturated content of the second heavy oil is preferably 60% by mass or more, more preferably 65% by mass or more, and even more preferably 70% by mass or more. If the saturated content is less than the lower limit, it is not preferable because the development of the bulk mesophase may be inhibited. The initial boiling point of the second heavy oil is preferably 200°C or higher, more preferably 250°C or higher. Also, the density of the second heavy oil at 15° C. is preferably 0.85 to 0.94 g/cm ³ . The second heavy oil is preferably obtained by hydrodesulfurizing heavy oil having a sulfur content of 2% by mass or more under conditions of a total pressure of 16 MPa or more so that the hydrocracking rate is 30% or less. It is hydrodesulfurized oil. The heavy oil, which is the raw material of the second heavy oil, has a sulfur content of 2% by mass or more, preferably 2.5% by mass or more, and more preferably 3% by mass or more.

The heavy oil with a sulfur content of 2% by mass or more is not particularly limited as long as the sulfur content satisfies the above conditions. Examples include visbreaking oil, tar sand oil, shale oil, and mixed oil thereof. Among these, atmospheric distillation residue and vacuum distillation residue are preferably used.

<Hydrodesulfurization to obtain the second heavy oil>
The hydrodesulfurization conditions for obtaining the second heavy oil are a total pressure of 16 MPa or higher, preferably 17 MPa or higher, and more preferably 18 MPa or higher. If the total pressure is less than the lower limit, cracking of the heavy oil by hydrodesulfurization proceeds excessively, making it impossible to obtain a heavy oil that is effective as a raw material for petroleum coke.

Conditions other than the total pressure in hydrodesulfurization are not particularly limited as long as the hydrocracking rate is 30% or less, but it is preferable to set various conditions as follows. That is, the hydrodesulfurization temperature is preferably 300 to 500° C., more preferably 350 to 450° C.; the hydrogen/oil ratio is preferably 400 to 3000 NL/L, more preferably 500 to 1800 NL/L. hydrogen partial pressure is preferably 7 to 20 MPa, more preferably 8 to 17 MPa; liquid hourly space velocity (LHSV) is preferably 0.1 to 3 h ⁻¹ , more preferably 0.15 to 1.0 h ^{− 1} , more preferably 0.15 to 0.75 h ⁻¹ . The catalyst (hydrodesulfurization catalyst) used for hydrodesulfurization includes Ni--Mo catalyst, Co--Mo catalyst, and catalysts in which both are combined. Commercially available products may be used.

<Heavy oil other than the first heavy oil and the second heavy oil>
In addition to the above-described first heavy oil and second heavy oil, the feedstock oil may contain other heavy oil and fluid catalytic cracking residual oil in a predetermined ratio. The fluid catalytic cracking residual oil in this case is a heavy oil that does not correspond to the first heavy oil and the second heavy oil, has a sulfur content of preferably 0.5% by mass or less, and has a bicyclic The heavy oil preferably contains 20% by mass or more of aromatic components, and examples thereof include fluidized catalytically cracked residual oil obtained by using vacuum desulfurized light oil as a raw material oil.

<Production of coking coal composition>
A raw material oil (mixed oil) containing at least the first heavy oil and the second heavy oil is coked at 400 to 600°C. Although the first heavy oil alone forms a good bulk mesophase, the amount of gas generated during solidification in the coking process is not sufficient, so the mesophase is not uniaxially oriented, and graphitization does not occur in the subsequent heat treatment. This is not preferable because it causes variations in the traveling speed. Therefore, the raw material oil includes at least the second heavy oil in addition to the first heavy oil. However, if the amount of the first raw material oil is too small, the 2- to 3-ring aromatic components generated by desulfurization of the "polycyclic aromatic components that are difficult to desulfurize" will be insufficient, and relatively small hexagonal mesh planes will be laminated on the bulk mesophase. It becomes difficult to sufficiently introduce the fine structure that has been processed. Therefore, based on the total amount of feedstock oil, the first heavy oil is limited to the range of 15 to 80% by mass. As a method for coking the raw material oil, a delayed coking method is preferable. Specifically, preferably, under the condition that the coking pressure is controlled, the raw material oil is put into a delayed coker, heated, thermally decomposed and polycondensed to produce a raw material coal composition.

<Manufacture of artificial graphite material>
The raw coal composition thus obtained is pulverized and classified to have a predetermined particle size. As for the particle size, the average particle size is preferably 41 μm or less. The average particle size is based on measurement with a laser diffraction particle size distribution meter. The reason why the average particle size is 41 μm or less is that the particle size is generally and preferably used as a negative electrode carbon material for lithium ion secondary batteries. Furthermore, the preferred average particle size is 5-41 μm. Since the specific surface area of the graphite material obtained by carbonizing raw coke with an average particle size of less than 5 μm is extremely large, a paste used in the manufacture of negative electrode plates for lithium ion secondary batteries using such a graphite material. In the case of producing a highly viscous fluid in the form of a liquid, the required amount of solvent becomes enormous, which is not preferable.

The carbonization method is not particularly limited, but usually heat treatment is performed in an inert gas atmosphere such as nitrogen, argon or helium at a maximum temperature of 900 to 1500 ° C. and a maximum temperature retention time of 0 to 10 hours. A method can be mentioned. Even if the carbonization step is omitted as necessary, there is almost no effect on the physical properties of the finally produced graphite material.

The graphitization method is not particularly limited, but usually, heat treatment is performed at a maximum temperature of 2500 to 3200 ° C. and a maximum temperature retention time of 0 to 100 hours in an inert gas atmosphere such as nitrogen, argon or helium. A method can be mentioned. It is also possible to enclose crushed green coke and/or calcined coke in a crucible and graphitize it in a graphitization furnace such as an Acheson furnace or an LWG furnace.

The artificial graphite material of the present invention can exhibit excellent characteristics even when used as it is as a negative electrode material for lithium ion secondary batteries, but other artificial graphite materials and natural graphite materials outside the scope of the present invention Even when mixed with, it exhibits excellent unique effects such as being able to suppress capacity deterioration when charging and discharging are repeated at 0 ° C. or less. The inventors found this effect and completed the third invention of the present application. Natural graphite-based materials refer to graphite-like materials produced from nature, high-purified graphite-like materials of the previous stage, spherical-shaped materials (including mechanochemical treatment), high-purity products and the surface of spherical-shaped products. is coated with another carbon (for example, pitch-coated products, CVD-coated products, etc.), plasma-treated products, and the like. The material used in the present invention may be scaly or spherical. The mixing ratio of the artificial graphite material of the present invention and other artificial graphite or natural graphite outside the scope of the present invention is 10:90 to 90:10, preferably 20:80 to 80:20, more preferably 20:80 to 80:20 by weight. 30:70 to 70:30.

[Negative electrode for lithium ion secondary battery]
Next, the negative electrode of the lithium ion secondary battery will be described. The method for producing a negative electrode for a lithium ion secondary battery is not particularly limited. ) to a predetermined dimension. As another method, the artificial graphite material of the present invention, a binder, a conductive aid, etc. are kneaded and slurried in an organic solvent, and the slurry is coated and dried on a current collector such as a copper foil, that is, a negative electrode. A method of rolling the material mixture and cutting it into a predetermined size can also be used.

Examples of the binder (binding agent) include polyvinylidene fluoride, polytetrafluoroethylene, and SBR (styrene-butadiene rubber). The content of the binder in the negative electrode mixture may be appropriately set to about 1 to 30 parts by mass with respect to 100 parts by mass of the artificial graphite material, depending on the design of the battery.

Examples of the conductive aid include carbon black, graphite, acetylene black, indium-tin oxide exhibiting conductivity, and conductive polymers such as polyaniline, polythiophene, and polyphenylene vinylene. The amount of the conductive aid used is preferably 1 to 15 parts by mass with respect to 100 parts by mass of the artificial graphite material.

Examples of the organic solvent include dimethylformamide, N-methylpyrrolidone, isopropanol, and toluene.

As a method for mixing the artificial graphite material, the binder, and optionally the conductive aid and the organic solvent, known apparatuses such as a screw kneader, a ribbon mixer, a universal mixer, and a planetary mixer can be used. The mixture is molded by roll pressing or press pressing, and the pressure at this time is preferably about 100 to 300 MPa.

As for the material of the current collector, any material can be used without particular limitation as long as it does not form an alloy with lithium. Examples include copper, nickel, titanium, and stainless steel. Also, the shape of the current collector can be used without any particular limitation. Porous materials such as porous metal (foamed metal) and carbon paper can also be used.

The method for applying the slurry to the current collector is not particularly limited, but examples include a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, Known methods such as a screen printing method and a die coater method can be used. After coating, it is common to carry out a rolling treatment using a flat plate press, calendar rolls, or the like, if necessary. Further, the integration of the negative electrode material slurry formed into a sheet-like, pellet-like shape, etc., and the current collector can be performed by a known method such as roll, press, or a combination thereof.

[Lithium ion secondary battery]
Next, the lithium ion secondary battery of this embodiment will be described.
FIG. 1 is a schematic cross-sectional view showing an example of the lithium ion secondary battery of the present invention. A lithium ion secondary battery 10 shown in FIG. 1 has a negative electrode 11 integrated with a negative electrode current collector 12 and a positive electrode 13 integrated with a positive electrode current collector 14 . The negative electrode of this embodiment is used as the negative electrode 11 in the lithium ion secondary battery 10 shown in FIG. The negative electrode 11 and the positive electrode 13 are arranged to face each other with the separator 15 interposed therebetween. In FIG. 1, reference numeral 16 indicates an aluminum laminate exterior. An electrolytic solution is injected into the aluminum laminate exterior 16 .

The positive electrode 10 includes an active material, a binder (binding agent), and optionally a conductive aid.
As the active material, known materials used for positive electrodes for lithium ion secondary batteries can be used, and metal compounds, metal oxides, metal sulfides, or conductive polymers capable of doping or intercalating lithium ions can be used. materials can be used. Specifically, active materials include, for example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), and composite oxides ( _{LiCo X} Ni _Y Mn ZO ₂ , X ₊ Y ₊ Z _{= 1} ), lithium vanadium compounds, _V2O5 , _V6O13 , _VO2 , _MnO2 , _TiO2 , _{MoV2O8 , TiS2} , _V2S5 , VS2, _MoS2 , _MoS3 , Cr ₃ O ₈ , Cr ₂ O ₅ , olivine-type LiMPO ₄ (M: Co, Ni, Mn, Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, porous carbon, etc., and mixtures thereof etc. can be mentioned.

As the binder, the same binder as that used for the negative electrode 11 can be used.
As the conductive aid, the same conductive aid as used for the negative electrode 11 can be used.
As the positive electrode current collector 14, the same one as the negative electrode current collector described above can be used.

As the separator 15, for example, a non-woven fabric, cloth, microporous film, or a combination thereof, which is mainly composed of polyolefin such as polyethylene or polypropylene, can be used.
If the lithium ion secondary battery has a structure in which the positive electrode and the negative electrode do not come into direct contact with each other, the separator is unnecessary.

As the electrolytic solution and electrolyte used in the lithium ion secondary battery 10, known organic electrolytic solutions, inorganic solid electrolytes, and polymer solid electrolytes used in lithium ion secondary batteries can be used.
As the electrolytic solution, it is preferable to use an organic electrolytic solution from the viewpoint of electrical conductivity.

Examples of the organic electrolyte include ethers such as dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and ethylene glycol phenyl ether, N-methylformamide, N,N-dimethylformamide, N - amides such as ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, dimethylsulfoxide, sulfur-containing compounds such as sulfolane, methyl ethyl ketone, dialkyl ketones such as methyl isobutyl ketone; cyclic ethers such as tetrahydrofuran and 2-methoxytetrahydrofuran; cyclic carbonates such as ethylene carbonate, butylene carbonate, propylene carbonate and vinylene carbonate; Chain carbonates, cyclic carbonates such as γ-butyrolactone and γ-valerolactone, chain carbonates such as methyl acetate, ethyl acetate, methyl propionate and ethyl propionate, N-methyl 2-pyrrolidinone, acetonitrile and nitromethane Organic solvents may be mentioned. These organic electrolytic solutions can be used alone or in combination of two or more.

Various known lithium salts can be used as the electrolyte.
For example, lithium salts include LiClO4, _LiBF4 , _LiPF6 , _LiAlCl4 , _LiSbF6 , _LiSCN , LiCl, _{LiCF3SO3 , LiCF3CO2} , LiN _{( CF3SO2} ) ₂ , _{LiN ( C2F5} SO ₂ ) ₂ and the like.

Polymer solid electrolytes include polyethylene oxide derivatives and polymers containing these derivatives, polypropylene oxide derivatives and polymers containing these derivatives, phosphate ester polymers, polycarbonate derivatives and polymers containing these derivatives, and the like.

Since the lithium-ion secondary battery 10 of the present embodiment includes the negative electrode 11 containing the artificial graphite material of the present embodiment, capacity deterioration is less likely to occur even when charge-discharge cycles are repeated at a low temperature of 0° C. or less. Therefore, the lithium ion secondary battery 10 of the present embodiment can be preferably used for industrial applications such as automobiles such as hybrid automobiles, plug-in hybrid automobiles and electric automobiles, and power storage for system infrastructure.

The lithium-ion secondary battery of the present invention may use the negative electrode of the present invention, and selection of members necessary for battery configuration other than the negative electrode is not subject to any restrictions.
Specifically, the structure of the lithium ion secondary battery of the present invention is not limited to the lithium ion secondary battery 10 shown in FIG.
The structure of a lithium-ion secondary battery is, for example, a structure in which a wound electrode group in which a strip-shaped positive electrode and a negative electrode are spirally wound with a separator interposed therebetween is inserted into a battery case and sealed. may Moreover, the structure of the lithium ion secondary battery may be a structure in which a laminated electrode plate group in which a plate-shaped positive electrode and a negative electrode are successively laminated via a separator is enclosed in an outer package.

The lithium-ion secondary battery of the present invention can be used as, for example, a paper-type battery, a button-type battery, a coin-type battery, a laminate-type battery, a cylindrical battery, a prismatic battery, and the like.

EXAMPLES The present invention will now be described in more detail with reference to examples and comparative examples. In addition, the present invention is not limited only to the following examples.

<Measurement of physical properties>
(1) Calculation of crystallite size L (112) of graphite powder Graphite powder was mixed with 10% by mass of Si standard sample as an internal standard, and a glass sample holder (window frame size 16 mm × 20 mm, depth 0.2 mm) and measured by wide-angle X-ray diffraction in accordance with JIS R7651 (2007) to calculate the crystallite size L (112) of the graphite powder. The X-ray diffractometer was ULTIMA IV manufactured by Rigaku Co., Ltd., the X-ray source was CuKα rays (using a Kβ filter Ni), and the voltage and current applied to the X-ray tube were 41 kV and 41 mA. The obtained diffraction pattern was also analyzed by a method conforming to JIS R7651 (2007). Specifically, after smoothing the measurement data and removing the background, it is subjected to absorption correction, polarization correction, and Lorentz correction. The (112) diffraction line was corrected to calculate the crystallite size L(112). The crystallite size was calculated using the following Scherrer's formula from the half width of the corrected peak. Measurement and analysis were performed three times each, and the average value was defined as L(112).
L=K×λ/(β×cos θB) Scherrer's formula where L: crystal size (nm)
K: form factor constant (=1.0)
λ: X-ray wavelength (=0.15416 nm)
θ: Bragg angle (corrected diffraction angle)
β: true half width (correction value)

(2) Measurement of volume-based surface area Particle size distribution was measured using a laser diffraction/scattering particle size distribution analyzer MT3300EXII manufactured by Microtrack Bell Co., Ltd. The dispersion liquid used for the measurement was prepared by mixing approximately 0.5 g of graphite powder with 0.1% by mass of sodium hexametaphosphate aqueous solution (several drops) and a surfactant (several drops) in a mortar until homogeneous. After combining, 41 mL of 0.1% by mass sodium hexametaphosphate aqueous solution was further added, and dispersed by an ultrasonic homogenizer. The measurement results of the obtained particle size distribution are described in JIS Z 8819-2 (2001) "Expression of particle size measurement results-Part 2: Calculation of average particle size or average particle diameter and moment from particle size distribution" It was calculated according to "5.5 Calculation of volume-based surface area".

(3) Measurement of oil absorption Measured and calculated in accordance with JIS K 5101-13-1 (2004) "Oil absorption - Section 1: Refined linseed oil method". First, accurately weighed graphite powder is placed on a measuring plate, and refined linseed oil is dropped from a 10 mL capacity buret, and the refined linseed oil is kneaded in with a palette knife to thoroughly knead, dropping and kneading. I repeated the call. Next, the end point was set when the paste became smooth and hard, and finally the oil absorption was calculated by the following formula.
O1 = 100 x V/m
where O1: oil absorption (mL00g)
V: volume of linseed oil dropped (mL)
m: Weight of graphite powder placed on the measuring plate (g)

(4) Measurement of ΔHpp (4.8K) 2.5 mg of graphite material was placed in a sample tube, and after evacuating with a rotary pump, the sample tube was filled with He gas and ESR was measured. The ESR device, microwave frequency counter, gauss meter, and cryostat used were ESP350E manufactured by BRUKER, HP5351P manufactured by HEWLETT PACKARD, ER035M manufactured by BRUKER, and ESR910 manufactured by OXFORD, respectively. X band (9.47 GHz) was used as the microwave, and the measurement was performed at an intensity of 1 mW, a central magnetic field of 3360 G, and a magnetic field modulation of 100 kHz. ESR measurement was performed at a measurement temperature of 4.8K. Table 1 shows the line width ΔHpp (4.8 K) of the ESR spectra of the graphite materials obtained in Examples and Comparative Examples. As the line width ΔHpp, a value obtained by reading the interval between two peaks (maximum and minimum) in the ESR spectrum (differential curve) was used. It was confirmed that the carbon-derived spectrum appearing in the electron spin resonance method measured using the X band was in the range of 3200 to 3400 gauss (G) in any of the examples and comparative examples.

<Production of artificial graphite material for lithium ion secondary battery negative electrode>
(Example 1)
Desulfurized vacuum gas oil (sulfur content 500 mass ppm, density 0.88 g / cm ³ at 15 ° C.) is subjected to fluid catalytic cracking, and fluid catalytic cracking residual oil (hereinafter referred to as “fluid catalytic cracking residual oil (A)”) is obtained. Obtained. The resulting fluid catalytic cracking residue (A) had an initial boiling point of 220° C., a sulfur content of 0.2% by mass, and an aroma component of 60% by mass. In addition, atmospheric distillation residue with a sulfur content of 3.5% by mass is hydrodesulfurized in the presence of a Ni—Mo catalyst so that the hydrocracking rate is 30% or less, and hydrodesulfurized oil (hereinafter referred to as Described as "hydrodesulfurized oil (A)"). The resulting hydrodesulfurized oil (A) had an initial boiling point of 260°C, a sulfur content of 0.3% by mass, an asphaltene component of 1% by mass, a saturated content of 70% by mass, and a density of 0.92 g/cm ³ at 15°C. there were.

Next, desulfurized vacuum gas oil (sulfur content 500 mass ppm, density at 15 ° C. 0.88 g / cm ³ ) and hydrodesulfurized oil (A) (initial boiling point 260 ° C., sulfur content 0.3 mass%, asphaltene component 1% by mass, 70% by mass of saturated content, density at 15 ° C. is 0.92 g / cm ³ ) are mixed at a mass ratio of 1:3, and then fluid catalytic cracking is performed to obtain fluid catalytic cracking residue (hereinafter referred to as “fluid catalytic cracking residue Oil (B)”) was obtained. The resulting fluid catalytic cracking residue (B) had an initial boiling point of 220°C, a sulfur content of 0.7% by mass, an aroma component of 80% by mass, a bicyclic aromatic component of 14% by mass, and a density at 15°C of 1.07 g/ ^cm3 .

Next, the following hydrodesulfurization system was used to hydrodesulfurize the fluid catalytic cracking residue (B). As catalysts, Catalyst 1, Catalyst 2 and Catalyst 3, which were produced as follows, were used.

[Production of catalyst 1]
A basic aluminum salt aqueous solution and an acidic aluminum salt aqueous solution were neutralized to obtain an alumina hydrate slurry (3 kg in terms of Al ₂ O ₃ ). The obtained alumina hydrate slurry was washed to remove the by-product salt to obtain an alumina hydrate. Alumina hydrate was adjusted to pH 10.5 and aged at 95° C. for 10 hours. After the aging, the slurry was dewatered and then concentrated and kneaded with a kneader to a predetermined moisture content to obtain an alumina kneaded product. 50 g of nitric acid was added to the obtained alumina kneaded product, and after concentration kneading to a predetermined moisture content again, it was formed into a cylindrical shape of 1.8 mm and dried at 110°C. The dried molded product was calcined at a temperature of 550° C. for 3 hours to obtain a carrier. The carrier composition is 100% by mass of alumina.

Next, 226 g of molybdenum trioxide and 57 g of basic nickel carbonate were suspended in ion-exchanged water, and 132 g of phosphoric acid was added to the suspension to obtain an impregnating solution. After drying this impregnated product, it was calcined at 550° C. for 1 hour to obtain the desired catalyst 1. The average pore size of the catalyst was measured to be 150 Å. The average pore diameter was measured by a mercury intrusion method, and is a value calculated using a mercury surface tension of 480 dyne/cm and a contact angle of 140°. The contents of nickel oxide and molybdenum oxide were 2.5% and 18% by weight, respectively, based on the catalyst.

[Production of catalyst 2]
In the carrier preparation, 100 g of nitric acid, 479 g of commercially available silica sol S-20L (manufactured by Nikki Shokubai Kasei Co., Ltd.), and 155 g of phosphoric acid were added to the obtained alumina kneaded product. got The carrier composition is 94 mass % alumina, 3 mass % silica, and 53 mass % P2O. In the preparation of the impregnating solution, the catalyst 2 was prepared in the same manner as the catalyst 1 except that 232 g of molybdenum trioxide, 23 g of basic nickel carbonate and 76 g of cobalt carbonate were used. The average pore size of the catalyst was measured to be 100 Å. The contents of nickel oxide, cobalt oxide and molybdenum oxide were 1%, 3.5% and 18% by weight, respectively, based on the catalyst.

[Production of catalyst 3]
1000 g of titanyl sulfate solution (5% by mass in terms of titania (TiO ₂ )), 1900 g of pure water and 370 g of sulfuric acid were mixed and stirred at 40° C. for 1 hour. It was added dropwise over 5 hours. After the dropwise addition was completed, stirring was continued at 40° C. for 2.5 hours. After adding 15 mass % aqueous ammonia to the resulting solution until the pH reached 7.2, the pH was kept at 7.2 for 2 hours to obtain a silica-titania primary particle-containing liquid. Next, the temperature of the silica-titania primary particle-containing liquid was adjusted to 60° C., and 25.6 kg of an alumina slurry containing boehmite (3.6% by mass in terms of alumina (AlO)) was added. 15% by mass aqueous ammonia was added so that the After maintaining the state of pH 7.2 for 1 hour, the slurry was dehydrated and washed to remove by-product salts, thereby obtaining an oxide gel slurry. After that, preparation was carried out in the same manner as for Catalyst 1 to obtain a carrier. The carrier composition is 92% by weight alumina, 3% by weight silica and 5% by weight titania. Catalyst 3 was obtained in the same manner as catalyst 1 except that 297 g of molybdenum trioxide, 74 g of basic nickel carbonate, and 101 g of phosphoric acid were used in the preparation of the impregnation solution. The average pore size of the catalyst was measured to be 75 Å. The contents of nickel oxide and molybdenum oxide were 3% and 22% by weight, respectively, based on the catalyst.

First, presulfurization was carried out in a flow-type fixed-bed reactor. Catalyst 1, Catalyst 2, and Catalyst 3 were charged in order of 20 ml, 50 ml, and 30 ml, respectively, in a flow-type fixed-bed reactor, and a mixed gas (hydrogen: hydrogen sulfide = 97% by volume: 3% by volume) was added at a flow rate of 30 L/hour. The reactor was heated from room temperature at a rate of 10° C./min under a total pressure of 6 MPa, held at 240° C. for 4 hours, and then heated again to 340° C. at a rate of 10° C./min. C. for 24 hours to complete the presulfurization.

After that, the fluid catalytic cracking residue (B) was passed through the flow-type fixed bed reactor at a rate of 70 ml / hour, the hydrogen partial pressure was 6 MPa, the liquid hourly space velocity was 0.7 h ⁻¹ , the hydrogen / oil ratio was 470 NL / L, and the reaction Hydrodesulfurization was carried out under reaction conditions of a temperature of 310° C. to obtain desulfurized fluid catalytic cracking residue (hereinafter referred to as “desulfurized fluid catalytic cracking residue (B-1)”). The resulting desulfurized fluid catalytic cracking residue (B-1) contained 28% by mass of bicyclic aromatic components. Next, the desulfurized fluid catalytic cracking residue (B-1) and the hydrodesulfurized oil (A) were mixed at a mass ratio of 80:20 to obtain a feed oil composition.

This raw oil composition was placed in a test tube and heat-treated at normal pressure and 500° C. for 3 hours to form coke to obtain a raw coal composition. This raw coal composition was pulverized with a hammer mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 22.9 μm. The resulting pulverized material was calcined at 1000° C. under nitrogen gas stream to obtain calcined coke. At this time, the temperature was raised from room temperature to 1000°C for 4 hours, the temperature was maintained at 1000°C for 4 hours, and the temperature was lowered from 1000°C to 410°C for 2 hours. It was allowed to cool for 4 hours. The obtained calcined coke was charged into a graphite crucible and graphitized at 2700° C. under a nitrogen gas stream using a high frequency induction furnace. At this time, the heating time from room temperature to 2700° C. was 23 hours, and the holding time at 2700° C. was 3 hours. The obtained graphite material was pulverized with an airflow jet mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 5.1 μm, to obtain an artificial graphite material. Table 1 shows the crystallite size L (112), volume-based surface area, oil absorption, and ΔHpp (4.8K) of the obtained artificial graphite material.

(Example 2)
The desulfurized fluid catalytic cracking residue (B-1), the fluid catalytic cracking residue (A) and the hydrodesulfurized oil (A) were mixed at a mass ratio of 15:65:20 to obtain a feed oil composition. This raw oil composition was placed in a test tube and heat-treated at normal pressure and 500° C. for 3 hours to form coke to obtain a raw coal composition. This raw coal composition was pulverized with a hammer mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 18.8 μm. The resulting pulverized material was calcined at 1000° C. under nitrogen gas stream to obtain calcined coke. At this time, the temperature was raised from room temperature to 1000°C for 4 hours, the temperature was maintained at 1000°C for 4 hours, and the temperature was lowered from 1000°C to 410°C for 2 hours. It was allowed to cool for 4 hours. The obtained calcined coke was charged into a graphite crucible and graphitized at 2800° C. under a nitrogen gas stream using a high frequency induction furnace. At this time, the heating time from room temperature to 2800° C. was 23 hours, and the holding time at 2800° C. was 3 hours. The obtained graphite material was pulverized with an airflow jet mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 13.2 μm, to obtain an artificial graphite material. Table 1 shows the crystallite size L (112), volume-based surface area, oil absorption, and ΔHpp (4.8K) of the obtained artificial graphite material.

(Example 3)
The desulfurized fluid catalytic cracking residue (B-1), the fluid catalytic cracking residue (A) and the hydrodesulfurized oil (A) were mixed at a mass ratio of 40:40:20 to obtain a feed oil composition. This raw oil composition was placed in a test tube and heat-treated at normal pressure and 500° C. for 3 hours to form coke to obtain a raw coal composition. This raw coal composition was pulverized with a hammer mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 20.5 μm. The resulting pulverized material was calcined at 1000° C. under nitrogen gas stream to obtain calcined coke. At this time, the temperature was raised from room temperature to 1000°C for 4 hours, the temperature was maintained at 1000°C for 4 hours, and the temperature was lowered from 1000°C to 410°C for 2 hours. It was allowed to cool for 4 hours. The obtained calcined coke was charged into a graphite crucible and graphitized at 2900° C. under a nitrogen gas stream using a high frequency induction furnace. At this time, the heating time from room temperature to 2900° C. was 23 hours, and the holding time at 2900° C. was 3 hours. The obtained graphite material was pulverized with an airflow jet mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 10.3 μm, to obtain an artificial graphite material. Table 1 shows the crystallite size L (112), volume-based surface area, oil absorption, and ΔHpp (4.8K) of the obtained artificial graphite material.

(Example 4)
The desulfurized fluid catalytic cracking residue (B-1), the fluid catalytic cracking residue (A) and the hydrodesulfurized oil (A) were mixed at a mass ratio of 30:50:20 to obtain a feed oil composition. This raw oil composition was placed in a test tube and heat-treated at normal pressure and 500° C. for 3 hours to form coke to obtain a raw coal composition. This raw coal composition was pulverized with a hammer mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 57.6 μm. The pulverized material thus obtained was placed in a graphite crucible, embedded in the Breeze of an Acheson furnace, and then graphitized at 3050°C. At this time, the heating time from room temperature to 3050° C. was 130 hours, and the holding time at 3050° C. was 8 hours. The resulting graphite material was pulverized with an airflow jet mill so as to have an average particle size of 29.8 μm as measured by a laser diffraction particle size distribution analyzer to obtain an artificial graphite material. Table 1 shows the crystallite size L (112), volume-based surface area, oil absorption, and ΔHpp (4.8K) of the obtained artificial graphite material.

(Example 5)
The desulfurized fluid catalytic cracking residue (B-1), the fluid catalytic cracking residue (A) and the hydrodesulfurized oil (A) were mixed at a mass ratio of 70:10:20 to obtain a feed oil composition. This raw oil composition was placed in a test tube and heat-treated at normal pressure and 500° C. for 3 hours to form coke to obtain a raw coal composition. This raw coal composition was pulverized with a hammer mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 44.2 μm. The pulverized material thus obtained was charged into a graphite crucible, embedded in the Breeze of an Acheson furnace, and then graphitized at 3150°C. At this time, the heating time from room temperature to 3150° C. was 130 hours, and the holding time at 3150° C. was 8 hours. The obtained graphite material was pulverized with an airflow jet mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 8.3 μm, to obtain an artificial graphite material. Table 1 shows the crystallite size L (112), volume-based surface area, oil absorption, and ΔHpp (4.8K) of the obtained artificial graphite material.

(Comparative example 1)
The desulfurized fluidized catalytic cracking residue (B-1) was placed in a test tube and heat-treated at 500° C. under normal pressure for 3 hours to form coke to obtain a coking coal composition. This raw coal composition was pulverized with a hammer mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 30.4 μm. The resulting pulverized material was calcined at 1000° C. under nitrogen gas stream to obtain calcined coke. At this time, the temperature was raised from room temperature to 1000°C for 4 hours, the temperature was maintained at 1000°C for 4 hours, and the temperature was lowered from 1000°C to 410°C for 2 hours. It was allowed to cool for 4 hours. The obtained calcined coke was charged into a graphite crucible and graphitized at 2700° C. under a nitrogen gas stream using a high frequency induction furnace. At this time, the heating time from room temperature to 2700° C. was 23 hours, and the holding time at 2700° C. was 3 hours. The obtained graphite material was pulverized with an airflow jet mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 4.8 μm, to obtain an artificial graphite material. Table 1 shows the crystallite size L (112), volume-based surface area, oil absorption, and ΔHpp (4.8K) of the obtained artificial graphite material.

(Comparative example 2)
The desulfurized fluid catalytic cracking residue (B-1), the fluid catalytic cracking residue (A) and the hydrodesulfurized oil (A) were mixed at a mass ratio of 10:60:20 to obtain a feed oil composition. This raw oil composition was placed in a test tube and heat-treated at normal pressure and 500° C. for 3 hours to form coke to obtain a raw coal composition. This raw coal composition was pulverized with a hammer mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 19.8 μm. The resulting pulverized material was calcined at 1000° C. under nitrogen gas stream to obtain calcined coke. At this time, the temperature was raised from room temperature to 1000°C for 4 hours, the temperature was maintained at 1000°C for 4 hours, and the temperature was lowered from 1000°C to 410°C for 2 hours. It was allowed to cool for 4 hours. The obtained calcined coke was charged into a graphite crucible and graphitized at 2800° C. under a nitrogen gas stream using a high frequency induction furnace. At this time, the heating time from room temperature to 2800° C. was 23 hours, and the holding time at 2800° C. was 3 hours. The obtained graphite material was pulverized with an airflow jet mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 12.1 μm, to obtain an artificial graphite material. Table 1 shows the crystallite size L (112), volume-based surface area, oil absorption, and ΔHpp (4.8K) of the obtained artificial graphite material.

(Comparative Example 3)
The desulfurized fluid catalytic cracking residue (B-1), the fluid catalytic cracking residue (A) and the hydrodesulfurized oil (A) were mixed at a mass ratio of 5:75:20 to obtain a feed oil composition. This raw oil composition was placed in a test tube and heat-treated at normal pressure and 500° C. for 3 hours to form coke to obtain a raw coal composition. This raw coal composition was pulverized with a hammer mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 29.7 μm. The resulting pulverized material was calcined at 1000° C. under nitrogen gas stream to obtain calcined coke. At this time, the temperature was raised from room temperature to 1000°C for 4 hours, the temperature was maintained at 1000°C for 4 hours, and the temperature was lowered from 1000°C to 410°C for 2 hours. It was allowed to cool for 4 hours. The obtained calcined coke was charged into a graphite crucible and graphitized at 2900° C. under a nitrogen gas stream using a high frequency induction furnace. At this time, the heating time from room temperature to 2900° C. was 23 hours, and the holding time at 2900° C. was 3 hours. The obtained graphite material was pulverized with an airflow jet mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 16.8 μm, to obtain an artificial graphite material. Table 1 shows the crystallite size L (112), volume-based surface area, oil absorption, and ΔHpp (4.8K) of the obtained artificial graphite material.

(Comparative Example 4)
The fluid catalytic cracking residue (A) was placed in a test tube and heat-treated at normal pressure at 500° C. for 3 hours to form coke to obtain a coking coal composition. This raw coal composition was pulverized with a hammer mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 38.6 μm. The pulverized material thus obtained was charged into a graphite crucible, embedded in the Breeze of an Acheson furnace, and then graphitized at 3150°C. At this time, the heating time from room temperature to 3150° C. was 130 hours, and the holding time at 3150° C. was 8 hours. The obtained graphite material was pulverized with an airflow jet mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 25.3 μm, to obtain an artificial graphite material. Table 1 shows the crystallite size L (112), volume-based surface area, oil absorption, and ΔHpp (4.8K) of the obtained artificial graphite material.

(Comparative Example 5)
The desulfurized fluid catalytic cracking residue (B-1) and the fluid catalytic cracking residue (A) were mixed at a mass ratio of 95:5 to obtain a feed oil composition. This raw oil composition was placed in a test tube and heat-treated at normal pressure and 500° C. for 3 hours to form coke to obtain a raw coal composition. This raw coal composition was pulverized with a hammer mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 52.2 μm. The pulverized material thus obtained was placed in a graphite crucible, embedded in the Breeze of an Acheson furnace, and then graphitized at 3050°C. At this time, the heating time from room temperature to 3050° C. was 130 hours, and the holding time at 3050° C. was 8 hours. The obtained graphite material was pulverized with an airflow jet mill so that the average particle size measured with a laser diffraction particle size distribution analyzer was 9.2 μm, to obtain an artificial graphite material. Table 1 shows the crystallite size L (112), volume-based surface area, oil absorption, and ΔHpp (4.8K) of the obtained artificial graphite material.

(Example 6)
A mixture of the artificial graphite material obtained in Example 3 and the artificial graphite material obtained in Comparative Example 2 at a weight ratio of 50:50 was obtained.

(Example 7)
A mixture of the artificial graphite obtained in Example 3 and the artificial graphite obtained in Comparative Example 2 at a weight ratio of 30:70 was obtained.

(Example 8)
A mixture of the artificial graphite obtained in Example 3 and the artificial graphite obtained in Comparative Example 2 at a weight ratio of 20:80 was obtained.

<Preparation of battery for evaluation>
A lithium ion secondary battery 10 shown in FIG. 1 was produced as an evaluation battery by the method described below. As the negative electrode 11, the negative electrode current collector 12, the positive electrode 13, the positive electrode current collector 14, and the separator 15, the following materials were used.

(Negative electrode 11, negative electrode current collector 12)
Any of the artificial graphite materials obtained in Examples 1 to 8 and Comparative Examples 1 to 5 and carboxymethyl cellulose (CMC (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a binder adjusted to a concentration of 1.5% by mass BSH-6)) and an aqueous solution in which styrene-butadiene rubber (SBR) as a binder is dispersed at a concentration of 48% by mass are mixed at a solid content mass ratio of 98:1:1, A paste-like negative electrode mixture was obtained. The obtained negative electrode mixture was applied to the entire surface of one side of a copper foil having a thickness of 18 μm as the negative electrode current collector 12, followed by drying and rolling. A negative electrode sheet formed on 12 was obtained. The coating amount of the negative electrode mixture per unit area on the negative electrode sheet was adjusted so that the mass of the graphite material was about 10 mg/cm ² .

After that, the negative electrode sheet was cut to have a width of 32 mm and a length of 52 mm. Then, part of the negative electrode 11 was scraped off in the direction perpendicular to the longitudinal direction of the sheet to expose the negative electrode current collector 12 that serves as a negative electrode lead plate.

(Positive electrode 13, positive electrode current collector 14)
Lithium cobaltate LiCoO ₂ (Cellseed C0N manufactured by Nippon Kagaku Kogyo Co., Ltd.) having an average particle size of 10 μm as a positive electrode material, polyvinylidene fluoride (KF#1120 manufactured by Kureha Co., Ltd.) as a binder, and acetylene as a conductive aid Black (Denka Black manufactured by Denka Co., Ltd.) was mixed at a mass ratio of 89:6:5, N-methyl-2-pyrrolidinone was added as a solvent, and kneaded to obtain a pasty positive electrode mixture. The obtained positive electrode mixture was applied to the entire surface of a 30 μm thick aluminum foil as the positive electrode current collector 14, dried and rolled, and the positive electrode 13, which is a layer made of the positive electrode mixture, became the positive electrode current collector. A positive electrode sheet formed on 14 was obtained. The coating amount of the positive electrode mixture per unit area on the positive electrode sheet was adjusted to be about 20 mg/cm ² in terms of mass of lithium cobaltate.

After that, the positive electrode sheet was cut to have a width of 30 mm and a length of 50 mm. Then, part of the positive electrode 13 was scraped off in the direction perpendicular to the longitudinal direction of the sheet to expose the positive electrode current collector 14 that serves as a positive electrode lead plate.

(Separator 15)
As the separator 15, a cellulose-based nonwoven fabric (TF40-50 manufactured by Nippon Kodo Paper Co., Ltd.) was used.

In order to manufacture the lithium ion secondary battery 10 shown in FIG. The positive electrode sheet integrated with the lead plate, the separator 15, and other members used in the lithium ion secondary battery 10 were dried. Specifically, the negative electrode sheet and the positive electrode sheet were dried at 120° C. for 12 hours or more under reduced pressure. Also, the separator 15 and other members were dried at 70° C. for 12 hours or more under reduced pressure.

Next, the dried negative electrode sheet, positive electrode sheet, separator 15 and other members were assembled in an argon gas circulation type glove box controlled so that the dew point was −60° C. or lower. As a result, as shown in FIG. 1, a single-layer electrode body in which the positive electrode 13 and the negative electrode 11 were laminated facing each other with the separator 15 interposed therebetween and fixed with a polyimide tape (not shown) was obtained. The negative electrode sheet and the positive electrode sheet were laminated such that the peripheral edge of the laminated positive electrode sheet was surrounded inside the peripheral edge of the negative electrode sheet.

Next, the single-layer electrode body was housed in the aluminum laminate sheath 16, and an electrolytic solution was injected inside. As the electrolytic solution, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte is dissolved in a solvent so as to have a concentration of 1 mol/L, and further vinylene carbonate (VC) is mixed so as to have a concentration of 1% by mass. I used something else. As a solvent, a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3:7 was used.
After that, the aluminum laminate exterior 16 was heat-sealed with the positive electrode lead plate and the negative electrode lead plate sticking out.
Through the above steps, sealed lithium ion secondary batteries 10 of Examples 1 to 8 and Comparative Examples 1 to 5 were obtained.

<Charging and discharging test of battery for evaluation>
The following charging/discharging tests were performed on the lithium ion secondary batteries 10 of Examples 1 to 8 and Comparative Examples 1 to 5, respectively.
First, a preliminary test was conducted to detect an abnormality in the battery. That is, the battery is placed in a constant temperature room at 25 ° C., charged at a constant current with a current of 4 mA until the battery voltage reaches 4.2 V, and after resting for 10 minutes, the battery voltage reaches 3.0 V at the same current. was discharged at a constant current until These charging, resting, and discharging were regarded as one charge/discharge cycle, and the charge/discharge cycle was repeated three times under the same conditions as a preliminary test.
This preliminary test confirmed that the batteries of Examples 1 to 8 and Comparative Examples 1 to 5 had no abnormalities. On that basis, the following final test was conducted. Note that the preliminary test is not included in the number of cycles of the main test.

In this test, the battery was placed in a constant temperature room at 25 ° C., the charging current was 30 mA, the charging voltage was 4.2 V, and the charging time was 3 hours. The battery was discharged at a constant current (30 mA) until the battery voltage reached 3.0V. These charging, resting, and discharging were regarded as one charging/discharging cycle, and the charging/discharging cycle was repeated three times under the same conditions.
Next, the battery was placed in a constant temperature bath set at 0° C. and left for 5 hours, after which the charge/discharge cycle was repeated 100 times under the same conditions as the charge/discharge cycle for determining the initial discharge capacity. After that, the battery was again placed in a constant temperature bath at 25 ° C. and left for 5 hours, and then the charge-discharge cycle was repeated three times under the same conditions as the charge-discharge cycle in which the initial discharge capacity was obtained. was defined as "discharge capacity after repeated charging and discharging at 0°C".

As an indicator of capacity deterioration after repeated charging and discharging at 0 ° C., the maintenance rate (%) of "discharge capacity after repeated charging and discharging at 0 ° C." with respect to the above "initial discharge capacity" is calculated as follows ( It was calculated using the formula 1).
Table 1 shows the results.

As shown in Table 1, the "discharge capacity retention rate (%) after repeated charging and discharging at 0 ° C." of the lithium ion secondary batteries using the artificial graphite material of Examples 1 to 5 for the negative electrode was 92%. On the other hand, in the case of the lithium ion secondary battery using the artificial graphite material of Comparative Examples 1 to 5 outside the scope of the present invention for the negative electrode, it is as low as 62.3 to 84.3%, 0 ° C. It was confirmed that deterioration was not suppressed when charging and discharging were repeated.

In addition, as shown in Table 1, the artificial graphite materials obtained in Examples 1 to 5 were made from raw oil compositions containing a specific first heavy oil and a specific second heavy oil as raw materials. in use. That is, a catalyst having an average pore diameter of 141 to 200 Å, in which the fluid catalytic cracking residue is filled with a catalyst supporting one or more metals selected from group 6A metals and group 8 metals of the periodic table on an inorganic oxide support. The layer (A) and the catalyst layer (B) having an average pore diameter of 65 to 110 Å are contacted in this order to obtain the first heavy oil hydrodesulfurized, and the first heavy oil and the sulfur content is 0.4% by mass or less, mixed with a second heavy oil that does not contain the first heavy oil, and the content of the first heavy oil is 15 to 80% by mass. A certain feedstock oil composition is obtained. A lithium-ion secondary battery using such an artificial graphite material for the negative electrode has suppressed capacity deterioration when charging and discharging are repeated at 0°C. On the other hand, it was also confirmed that deterioration was not suppressed in the lithium ion secondary batteries using the negative electrodes of Comparative Examples 1 to 5, which were manufactured using raw material oil compositions other than those described above.

On the other hand, a mixture of the artificial graphite material obtained in Example 3 and the artificial graphite material obtained in Comparative Example 2 at a weight ratio of 50:50, 30:70, or 20:80 is used for the negative electrode. The lithium-ion secondary batteries thus obtained had capacity retention rates of 91.3%, 90.8% and 89.5%%, respectively, even after 100 cycles of charging and discharging at 0°C. The same capacity retention rate of the lithium ion secondary battery in which the artificial graphite material of Example 3 was used alone for the negative electrode was 94.7%, and in the case of Comparative Example 2, it was 62.3%. It was confirmed that fertility was not established. Although the reason for this is not clear, the lithium ions once occluded by the artificial graphite of Example 3 are occluded by the artificial graphite of Comparative Example 2 only by diffusion in the solid phase without going through the liquid phase (electrolytic solution). The possibility was also considered. From the above, it was confirmed that the lithium ion secondary battery using the negative electrode containing at least the artificial graphite material of the present invention can suppress the deterioration of the discharge capacity due to repeated charge-discharge cycles at 0°C.

A lithium ion secondary battery having a negative electrode containing the artificial graphite material according to the present invention is less likely to deteriorate in discharge capacity due to repeated charging and discharging at 0°C. Therefore, the lithium ion secondary battery of the present invention can be preferably used for automobiles such as hybrid automobiles, plug-in hybrid automobiles and electric automobiles, and for industrial purposes such as power storage for system infrastructure.

10 lithium ion secondary battery, 11 negative electrode, 12 negative electrode current collector, 13 positive electrode, 14 positive electrode current collector, 15 separator, 16 aluminum laminate exterior.

Claims (4)

The crystallite size L (112) in the c-axis direction calculated from the (112) diffraction line obtained by X-ray wide-angle diffraction is 4 to 30 nm,
A volume-based surface area calculated by a laser diffraction particle size distribution analyzer is 0.22 to 1.70 m ² /cm ³ ,
an oil absorption of 67 to 147 mL/100 g,
The spectrum derived from carbon that appears in the electron spin resonance method measured using the X band is in the range of 3200 to 3410 gauss, and the line width of the spectrum calculated from the first derivative spectrum at a temperature of 4.8 K of the spectrum. △Hpp is 41 to 69 gauss
An artificial graphite material characterized by: A method for producing the artificial graphite material according to claim 1,
a step of coking the raw oil composition by a delayed coking process to produce a raw coal composition;
a step of pulverizing the raw coal composition to obtain raw coal powder;
a step of heat-treating the raw coal powder to obtain graphite powder;
at least a step of pulverizing the graphite powder ,
A catalyst layer having an average pore diameter of 141 to 200 Å, in which the fluid catalytic cracking residue is filled with a catalyst supporting one or more metals selected from group 6A metals and group 8 metals of the periodic table on an inorganic oxide support ( A) and a catalyst layer (B) having an average pore size of 65 to 110 Å in this order to obtain a hydrodesulfurized first heavy oil;
A step of mixing the first heavy oil and a second heavy oil having a sulfur content of 0.4% by mass or less and not containing the first heavy oil to obtain a feedstock oil composition. and further comprising
A method for producing an artificial graphite material, wherein the content of the first heavy oil in the raw oil composition is 15 to 80% by mass . A negative electrode for a lithium ion secondary battery, comprising the artificial graphite material according to claim 1 . A lithium ion secondary battery comprising the negative electrode according to claim 3 .

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